The distribution of rotavirus VP7 serotypes circulating in four locations in Malaysia, representing three geographical areas, was examined using 341 RNA-positive stool specimens obtained discontinuously between 1977-88 from hospitalized children below the age of five years suffering from acute gastroenteritis; the majority of specimens (70%) originated from 1988. A total of 306 specimens (256 stool suspensions and 50 tissue culture-adapted strains) were confirmatory ELISA-positive and were tested in a serotype ELISA utilizing monoclonal antibodies to rotavirus serotypes 1, 2, 3, 4, and 9. A total of 59% could be serotyped. Their serotype distribution demonstrated an overall predominance of rotavirus serotype 4 in Malaysia (71%), followed by serotype 1 (15%); serotypes 2 (4%) and 3 (4%) were rare. No serotype 9 rotavirus was detected, and eleven specimens (6%) displayed multiple serotype reactivities. Rotavirus serotype 4 predominated in 1988 in the three West Malaysian locations, while a more even serotype distribution was observed among a limited number of specimens from an East Malaysian location. Serotype 4 also predominated in Kuala Lumpur in 1987; limited data suggested the possible predominance of serotype 1 in this location in earlier years. All 341 specimens were also passaged twice in AGMK cells for tissue vulture adaptation, followed by one passage in MA-104 cells. The VP4 types of all specimens that were successfully adapted to growth in MA-104 cells was determined by molecular hybridization of northern-blotted RNA to PCR generated probes representing the hyperdivergent region of the VP8 portion of the VP4 genes of rotavirus strains KU, DS-1, 1076, and K8 (VP4 serotypes 1A, 1B, 2, and 3, respectively). The majority (123) of specimens tested hybridized with the KU probe, three specimens hybridized specifically with the K8 probe, and none hybridized to the 1076 probe.